In recent years, regulations are increasingly strengthened on a biological test and a clinical test conducted for the sake of treatment of human diseases. As an alternative for the biological test and the clinical test, research and development have been extensively made on the collection of live cells from the human blood. The collection of cells is conducted by different kinds of cell collecting devices such as a micro-fluidic device, a CTC (Circulating Tumor Cell) chip, a filter, and so forth.
A filter for filtering cells from blood is disclosed in many patent documents, e.g., U.S. Patent Publication Nos. 2007/0025883A1 and 2009/0188864A1. The filter is formed of a membrane having a plurality of pores for filtering cells. In the technologies of the aforementioned patent documents, cancer cells are dispersed over the entire surface of the filer mounted inside a chamber or a central square hole. For that reason, there is a problem in that it becomes difficult to identify the filtered state of the cancer cells. Moreover, it is difficult to recover and collect the cancer cells dispersed on the surface of the filter.